An aerosol delivery system is disclosed that is a single-use (disposable) continuous nebulizer system designed for use with mechanically ventilated patients to aerosolize medications for inhalation with a general purpose nebulizer, or for connection with devices usable in endoscopic procedures. The system separates the liquid reservoir from the nebulization process taking place either at the adapter hub, where it fits into an endotracheal tube (ETT), or a gas humidifier, where the aerosol may treat a gas used in an endoscopic procedure, with a multi-lumen tube configured to nebulize liquid and air at its distal end. The refillable liquid reservoir is mounted away from the immediate treatment zone, avoiding orientation issues associated with other types of nebulizers having a self-contained reservoir. The system can produce aerosols having a wide range of droplet sizes, depending upon central lumen diameter, with values of MMAD that range from 4 to 30 μm.